1. Field of the Invention
The present invention relates to a sound reproduction method and sound reproduction system suitable for use in playing back audio signals including a low frequency audio signal in multichannel sound reproduction such as 5.1-channel sound reproduction.
2. Description of the Related Art
Video-and-audio playback systems, called “home theater systems”, are coming into widespread use. In the video-and-audio playback systems, by using relatively-large-screen displays to display video playback from, for example, DVDs (digital versatile discs), and, by recently employing 5.1-channel sound reproduction as multichannel reproduction for audio playback, exciting video and audio can be played back.
A 5.1-channel sound reproduction system needs four types of speakers, that is, front speakers, a center speaker, rear speakers, and a subwoofer. The subwoofer, which is used for low frequencies, originally reproduces a frequency range of 100 Hz or less. The other speakers reproduce frequencies from 100 Hz to 20 kHz.
Speaker arrangement of the related art in the 5.1-channel sound reproduction system is as shown in FIG. 21. Specifically, as shown in FIG. 21, in front of a listener 1, a front left channel speaker 2FL is disposed on the left side, a front right channel speaker 2FR is disposed on the right side, and a center channel speaker 2C is disposed opposing the listener 1.
Behind the listener 1, a rear left channel speaker 2RL is disposed on the left side and a rear right channel speaker 2RR is disposed on the right side. In addition, a subwoofer 2SW for an LFE (low frequency effect) channel (only for low frequencies) is disposed at an appropriate position.
These six speakers 2FL, 2FR, 2C, 2RL, 2RR, and 2SW are disposed at their positions, with them provided in speaker boxes. In general, in many cases, the six speakers around the listener 1 are disposed so that each (indicated by “ds”) of distances between the listener 1 and the six speakers is, for example, approximately two meters.
In a sound reproduction system of the related art, speaker boxes each having a volume of, for example, approximately 15 liters, are used for left and right speakers. The speaker boxes have changed to small boxes each having a volume of approximately one liter. Left and right speakers for which such small boxes are used are also called “satellite speakers”. Obviously, the left and right speakers do not reproduce any low frequencies. Accordingly, a speaker called a “subwoofer” only for low frequencies is additionally used in order to supplement the reproduction. As described above, when small boxes are used for the speakers other than the subwoofer, it is common that a cross-over frequency of an audio signal supplied to the subwoofer 2SW is 150 Hz, which is slightly higher than the frequency of 100 Hz. Nevertheless, the fact remains that the frequency of 150 Hz is considerably low.
By using a speaker system having the above-described arrangement to play back 5.1-channel audio signals from a DVD, obviously, sufficiently low frequency sounds are reproduced. In addition, since a reproduction channel is specially provided only for low frequency sounds, when a movie sound or the like is used as a sound source, uncommon deep bass resonates across an entire room, thus enabling the listener to have exciting realistic sensation.
In general, high frequency sounds are easily insulated. Accordingly, a single wall or door can considerably attenuate most of the high frequency sounds. However, sound insulation is not easy for low frequency sounds having, for example, 100 Hz or less, which are to be reproduced by the subwoofer. In many cases, in small houses, it is difficult for a room to have a size for insulating the low frequency sounds. In addition, in order for common 5.1-channel speaker arrangement to reproduce exciting sounds when enjoying DVD video and audio, a sound volume of approximately 90 dB or greater is necessary. In this reproduction, in particular, low frequency sounds, such as 50 Hz and 40 Hz, reproduced by the subwoofer, resonate to propagate in a wide range.
Therefore, there is a possibility that, when sounds are reproduced from the subwoofer in a room, the reproduced sounds reach not only the next room but also even upstairs and downstairs rooms, thus causing trouble. In particular, as the sounds have lower frequencies, it is more difficult to insulate the sounds. Using the subwoofer is a big problem in the housing situation in urban areas, so that it is actually difficult to sufficiently utilize the 5.1-channel sound reproduction system.
To solve this problem, Japanese Unexamined Patent Application Publication No. 05-95591 discloses a sound reproduction system in which intermediate and high frequency sounds are reproduced by using small speakers and low frequency sounds are reproduced in the vicinity of listener's ears by using a pair of low-frequency-sound headphones or bone conduction.
According to the sound reproduction system disclosed in Japanese Unexamined Patent Application Publication No. 05-95591, sound reproduction is performed, with low frequency sounds reproduced in the vicinity of listener's ears by using low-frequency-sound headphones or bone conduction. Thus, although the reproduced sounds can be heard as loud, the reproduced sounds can be prevented from being conducted to a neighboring house.